Storage tube and target element therefor having an irregular surface



Nbv. 16, 1965 A. S. JENSE STORAGE TUBE AND TARGET ETAL EMENT THEREFOAVING AN IRREGULAR SURFACE Filed Sept. 6. 1961 Fig.6.

ATToNEY United States Patent 3,218,496 STORAGE TUBE AND TARGETELEI'VHENT THERE- FOR HAVING AN IRREGULAR SURFACE Arthur S. Jensen,Baltimore, and Walter G. Reininger, Catonsville, Md, assignors toWestinghouse Electric Corporation, East Pittsburgh, Pin, a corporationof Pennsylvania Filed Sept. 6, 1961, Ser. No. 136,330 12 Claims. (Cl.313--67) This invention relates generally to electron discharge devicesand more particularly to improved storage targets for use in cathode raytype memory tubes.

In the conventional electrostatic storage tube, information is writtenonto the surface of a dielectric target by means of an electron beam(writing beam) and is stored in the form of charges established on thesurface of that target. The establishment of these charges may beaccomplished either by secondary emission effect or by inducing acurrent within the dielectric by electron bombardment. Both thesemethods of establishing the charge are well known in the art.

A reading beam is then utilized to scan the target and derive an outputin accordance with the charge information. In one form of storage tubethe entire surface of the storage target upon which the reading beam isincident is a dielectric. Upon its impingement, the reading beam removesthe stored charge, returning the surface close to a common referencepotential, as in a vidicon the differential charge removed is coupledcapacitively to an output signal amplifier, or as in an image orthiconthe return beam, deficient by the differential charge deposited, iscollected and amplified. The preferred method of reading utilizes astorage target surface which is approximately 50% dielectric and 50%interconnected conductor. The reading beam electrons approach thestorage target slowly, having only about one or two electron-voltsenergy when they impinge upon the conductor areas. The dielectric areasare just sufficiently negative that the reading beam electrons cannotland on them. The stored signal charges are such that they make theareas where they are located still more negative. These negative areasact as a coplanar grid to modulate the amount of the reading beam whichimpinges upon the conductor areas. Either this differential currentwhich impinges upon the conductor areas can be amplified or thereflected return beam deficient by this differential current can becollected and amplified. This preferred reading operation is thatutilized by Louis Pensak in US. Patent 2,728,020 and The Metrechon-AHalftone-Picture Storage Tube, RCA Review, vol. XV, No.2, pp. 145-162,June 1954.

In order that information stored on the target be faithfully retained,it is necessary that no extraneous charging or discharging be allowed toaffect the dielectric target surface. In the case of a storage target ofthe tape variety, which is designed to be wound upon itself to permit amultiplicity of storage areas to be sequentially utilized, the problembecomes particularly acute. Frictional or triboelectric effectsresulting from the reeling and unreeling of the tape itself and from thetape running over such elements as idler pulleys may produce sufficienttriboelectric charge to impair seriously the quality of the informationstored on the dielectric target. In addition, contact of the storagesurface with the back of the successive "layer of tape may permit thecharged area to discharge to the back of that layer, thus affecting thestored information.

It has been suggested in the prior art, see for example RCA TechnicalNote No. 45, Tape Storage Tube, by Arthus S. Jensen, that a tape beconstructed of a flexible dielectric storage strip or tape, one side ofwhich is coated with a thin conducting layer. A fine metallic mesh orgrid Patented Nov. 16, 1965 is then applied to the other side which,inter alia, serves to prevent the back of subsequent layers of tape fromcoming into contact with the dielectric storage surface when the tape isbeing reeled or unreeled. Tapes of this nature have proven to begenerally unsatisfactory. As the metallic grid or mesh positioned on thedielectric surface is generally in the order of 1 micron thick, dustparticles or slight irregularities in the conducting layer on the backof the subsequent layer of tape will bring this layer into contact withthe dielectric storage surface. This contact is detrimental from twoaspects. First of all, this contact permits the discharging of thestored information from the dielectric surface to the conducting layerof the subsequent layer of tape. Secondly, this contact may producefrictional or triboelectric charges during the reeling and unreeling ofthe tape. The accumulative effect of the discharging to the metalliclayer and that of the triboelectric charges may be sufficient to destroythe resolution of the information stored upon the dielectric targetsurface.

It is, therefore, an object of this invention to provide a cathode raytype memory tube having an improved storage target.

A further object of this invention is to provide an improved tape typestorage target adapted to be wound upon itself.

A still further object of this invention is to provide a tape storagetarget in which the contact of the storage surface with subsequentlayers of storage tape is reduced to a minimum.

Another object of this invention is to provide an improved storagesurface for a dielectric target.

Still another object of this invention is to provide an improvedelectrostatic storage target which is easy and economicai to manufactureand which possesses a high degree of resolution.

Stated briefly, the tape storage target in accordance with the presentinvention comprises a supporting structure having a roughened surfacewith a dielectric storage material disposed upon a portion of theroughened surface. The dielectric material is positioned so that it liesin planes or on surfaces which are transverse to the plane of the tape.This positioning of the dielectric material reduces the possible area ofcontact with subsequent layers of tape and serves to prevent spuriouscharging and discharging of the storage elements.

Further objects and advantages of the invention will be come apparent asthe following description proceeds and features of novelty whichcharacterize the invention will be pointed out in particularity in theclaims annexed to and forming a part of this specification.

For a better understanding of the invention, reference may be had to theaccompanying drawings, in which:

FIGURE 1 is a schematic view of a cathode ray tube utilizing the presentinvention;

FIG. 2 is a side elevational view, in section, showing an enlargedportion of the storage target embodied in FIG' 1;

FIG. 3 is a top plan view of a target shown in FIG. 2;

FIG. 4 is a top plan view showing a first embodiment of the storagetarget embodied in FIG. 1;

FIG. 5 is a cross sectional view of an embodiment of FIG. 4 taken alongthe line VV of FIG. 4;

FIG. 6 is a side elevational view, in section, showing anotherembodiment of the present invention;

FIG. 7 is an end view, in section showing a further modification of thepresent invention; and

FIG. 8 is a side elevational view, in section, of a further embodimentof the present invention, in which the dielectric storage elements arerandomly spaced.

Referring to FIG. 1, the memory tube comprises an envelope 11 of glassor other suitable material within which is positioned an electron gun,indicated generally at 2, for forming and focusing an electron beam upona storage target 31. The beam electrons are produced by a thermioniccathode 13 and are controlled by an apertured control grid 15. Anaccelerating electrode 17 is positioned in alignment with the beam andaccelerates the electrons emitted from the cathode 13. Elements 19, 21and 23 are electrodes which serve to focus the accelerated electronsinto a defined beam. Pairs of vertical and horizontal deflection plates,25 and 27 respectively, direct the beam to particular elemental regionson the surface of the target 31. Cylindrical electrodes 55, 57 and 59form a collimating lens which insures that the electron beam impingesperpendicularly upon a decelerator grid 29 and the storage target 31.The decelerator grid 29, located in close proximity to the target, isbiased several volts positive with respect to the potential of thetarget 31 and serves to collect secondarily emitted electrons during theerasing, priming and writing operations. The decelerator grid 29 alsoserves in the establishment of a uniform electric field in the targetarea which decelerates the incident reading beam electrons from a highenergy level at the grid 29 to a lower level of from zero toapproximately two volts in close proximity to the storage target 31. Theabove elements are supported within the tube and are connected tosuitable sources of voltage, which have not been shown, by suitableleads (also not shown) extending and sealed through the envelope 11.

Although the target may be fixed and rigid if the device is to beoperated as a conventional storage tube, e.g. for scan conversion, thespecific embodiment of FIG. 1 shows the target 31 to be of the flexibletape variety which is disposed within the envelope 11 at the oppositeend from the electron gun assembly 2 and positioned so as to be actedupon by the electron beam. The tape 31 is preferably wound upon reelswhich are driven by means, which have not been shown, external to theenvelope.

With reference to FIG. 2, there is shown a storage target 31 which maybe of the tape variety, such as is utilized in the structure of FIG. 1and which embodies the present invention. A base layer 33, which may bea polyester resin such as that sold by E. I. du Pont de Nemours andCompany under the trade name Mylar, is debossed on one surface. Thisdebossing may be achieved by bringing the base 33 into pressure contactwith a steel roller having a series of grooves or lenticulations in theform of substantially straight line debossments formed into its surfaceparallel to its axis. The base 33 then receives uniformly thickconducting coatings 35 and 37. on both sides, which may be metal whichhas been deposited by vacuum evaporation. The debossed side is thenuniformly coated with a dielectric material such as magnesium fluorideto form another layer 39 which is approximately one micron thick andlies in planes which are transverse to the plane of the tape. By virtueof the uniform thickness of the layers 37 and 39, the debossed groovesof the base 33 are carried through to the surface of the dielectriclayer 39. By suitable means, such as shadow evaporation, one side of thegrooves in the layer 39 receives a coating 41 of conductive material toform bars which are a part of a grid network as is shown in FIG. 3. Afurther evaporation deposits two Conducting strips 43 lengthwise nearthe edges of the tape which serve to connect electrically the grid bars41.

The tape as is shown in FIG. 2 may be utilized for electron bombardmentinduced conductivity (EBIC) writing. The conducting layer 37 serves totake up the electrons of the primary beam and the electrons from thedischarge of the dielectric surface during writing as well as providingfor biasing during the priming period of the target. The grid assemblycomprising the conducting bars 41 and strips 43 prevents redistributionof charges by secondary emission effect during the writing period.Information is stored on surface elements 47 of the dielectric material39. As may be readily seen, if the tape shown in FIG. 2 is wound uponitself, the conducting layer 35 contacts only the grid structure 41, 43.Any triboelectric charges generated during the reeling or unreeling, orby movement of the tape over pulleys, etc. within the system, areeffectively removed by the conducting layer 35 and grid assembly 41, 43.Also, by disposing the storage elements 47 within the recesses formed bythe grooved structure, there is little opportunity for the contact ofthese elements with subsequent layers of tape and hence little changefor the drainage of stored information from the storage elements tosubsequent'layers of tape.

While the above structure was described with respect to electronbombardment induced condutivity (EBIC) writing, it is readily apparentthat the target structure would be equally effective for secondaryemission writing. if secondary emission writing were used, however, theconducting layer 37 would not be necessary.

A simplified embodiment of this invention is shown in FIGS. 4 and 5. Thetape 31 of this embodiment comprises a conducting strip 49, such asstainless steel or copper, which is debossed by a series of groovesparallel to the length of the tape. The debossing may be accomplishedeither by pressure contact or electro-forming with a roller havinggrooves formed circumferentially in its surface. After the debossing ofthe steel tape has been accomplished, a suitable dielectric storagematerial 51, such as manganese fluoride, is shadow evaporated onto oneface of the groove so that, as previously stated, the dielectric lies inplanes or on surfaces which are transverse to that of the tape. Thisdielectric material forms elemental areas for the storage of informationeither by EBIC or secondary emission writing. While it is evident thatin this embodiment the dielectric material will come into contact withthe bottom of subsequent layers of the stainless steel or copper tapewhen the tape is wound upon itself, it is not that the area of contactis very small. Because of this small contact area, the amount ofinformation discharged from the storage areas 51 to the subsequent baselayer 49 is insignificant. Also, because of the small area of contact,no significant triboelectric effects will be generated.

The embodiment shown in FIG. 6 differs only from that of FIGS. 4 and 5insofar as the grooves are formed perpendicular to the length of thetape. From this, it is evident that the direction of the grooves isunimportant and that they may be formed at any angle to the length ofthe tape.

A further modification of the present invention which incorporatesfeatures of the preceding embodiments is illustrated in FIG. 7. Here,the grooved base layer 33 is again made of a plastic such as Mylar, and,as has been previously stated, the grooves may be positioned at anyangle with respect to the length of the tape. A uniformly thickconducting layer 35 is then applied to the underneath side of the layer33 and incremental storage element 51 of dielectric storage material aredeposited, preferably by means of shadow evaporation to a portion of thegroove faces. The operation of the target of this modification is thesame as that described with respect to the previous embodiments.

The embodiment shown in FIG. 8 differs from that shown in FIGS. 4through 6, in that, the regular groove structure of the earlier figuresis replaced by randomly spaced depressions 53, of irregular size, withinthe surface of the steel tape 49. These randomly spaced depressions maybe formed by sandblasting, abrading or by any other suitable method. Thedielectric material 51, however, is again shadow evaporated onto only aportion of the exposed roughened surface which is transverse to theplane of the tape. While the structure of this embodiment possesses alower resolution than those of the preceding embodiments, in which thestorage elements were disposed in the regular pattern, the structure ismore economical to manufacture and has a resolution which is sufiicientfor many applications.

While there have been shown and described what are presently consideredto be the preferred embodiments of the invention, modifications theretowill readily occur to those skilled in the art. Although the type ofstructure has been described mainly with reference to an elongated tape,it is apparent that a section of the tape will serve equally well as astationary target. It is not desired, therefore, that the invention belimited to the specific arrangement shown and described and it isintended to cover in the appended claims all such modifications as fallwithin the true spirit and scope of the invention.

We claim as our invention:

1. A storage target comprising a base member having a roughened surfaceand a coating of dielectric storage material in contact with saidroughened surface, said dielectric material being disposed in portionsof the roughened surface which are transverse to the plane of said basemember and so that the exposed surface of said dielectric materialsubstantially follows the contour of said roughened surface.

2. A storage target comprising a base member having a plurality ofirregularities disposed within one face of said base member, a coatingof dielectric storage material disposed upon portions of saidirregularities, a substantial portion of the exposed surface of saiddielectric storage material being disposed beneath a plane defined bythe points of maximum height of said irregularities.

3. A storage tape comprising a base member having a surface with aplurality of depressions therein, and a discontinuous coating ofdielectric storage material disposed upon portions of saidirregularities, the exposed surface of said dielectric material beingdisposed in planes transverse to the plane of said base member.

4. An elongated, flexible storage tape comprising a base member, aseries of parallel grooves disposed within one surface of said basemember, said grooves extending substantially parallel to the length ofsaid tape, and a coating of dielectric storage material in contact witha portion of the faces of said grooves, said dielectric material beingdisposed on said portions which are transverse to the plane of said basemember and so that the surface of said dielectric storage materialsubstantially follows the surface of said faces of said grooves.

5. An electrostatic storage target comprising a base member having onesurface thereof roughened, said roughened surface comprising a pluralityof depressions, said depressions having points of maximum height whichdefine a plane, and dielectric storage material disposed upon portionsof said roughened surface, said dielectric material being disposed onportions of the roughened surface which are transverse to said plane andso that a major portion of the exposed surface of said dielectricmaterial lies beneath said plane.

6. A method of constructing a storage target comprising the steps ofproviding a base member having one side thereof roughened and shadowevaporating a discontinuous coating of dielectric storage material ontosaid roughened surface, said evaporation being performed from an angleacute to the surface of said base member to provide that only thoseportions of the roughened surface disposed in planes opposed to thedirection of incident vapor are coated, the remaining surfaces remainingexposed.

7. A method of constructing an electrostatic storage target comprisingthe steps of providing a base member having a plurality of groovesformed in one surface thereof and disposing by shadow evaporation acoating of dielectric storage material on a portion of the surface ofsaid grooves, said shadow evaporation performed from an angle acute tothe surface of said base member to provide dielectric material only onthose surfaces which lie in a plane opposed to the direction of incidentvapor, theremaining surfaces remaining exposed.

8. A cathode ray storage tube comprising an envelope, means within saidenvelope for forming an electron beam along a path, a storage targetwithin said envelope positioned transverse to said beam, said targetcomprising a base member having one surface with a plurality ofdepressions therein, said depressions having points of maximum heightwhich define a plane, and a discontinuous coating of dielectric storagematerial affixed to said roughened surface so that a major portion ofthe exposed surface of said dielectric material lies beneath said plane.

9. A cathode ray storage tube comprising an envelope, means within saidenvelope for forming a beam along a path, a storage target within saidenvelope positioned transverse to said beam, said storage targetcomprising an elongated, flexible tape positioned about a dispensingmeans, said tape having a plurality of depressions, and a layer ofdielectric storage material disposed in contact with a portion of thefaces of said grooves which lie in a plane transverse to the plane ofsaid base member.

10. An elongated storage tape comprising an electrical- 1ynon-conductive strip having first and second major surfaces, a firstelectrical conductive layer in contact with the first of said majorsurfaces, at second electrical conductive layer of even thickness incontact with the second of said major surfaces and a layer of dielectricmaterial of even thickness for the storage of electrostatic charges incontact with said second conductive layer, a series of substantiallyparallel grooves formed in the exposed face of said dielectric material,a series of electrical conductive bars in contact with one correspondingface of each of said grooves and means for electrically connecting saidbars.

11. An elongated tape for the storage of electrostatic chargescomprising a first non-conductive strip having first and second majorsurfaces, a first layer of conductive material in contact with the firstof said major surfaces, a plurality of substantially parallel groovesformed in said second major surface, a second conductive layer ofsubstantially constant thickness in contact with said second majorsurface and a layer of dielectric storage material of substantiallyconstant thickness in contact with said second conductive layer toprovide a grooved surface in said dielectric layer, a series ofconductive strips in contact with a portion of the groove walls andextending upwardly beyond said dielectric and at least one conductivestrip extending substantially perpendicular to said series of conductingstrips to electrically connect said series of conductive strips.

12. A storage target comprising an electrically nonconductive base, aplurality of grooves formed within one side of said base member, thepeaks of said grooves defining a plane, a uniformly thick electricalconductive layer in contact with the opposed side of said base layer,and a discontinuous coating of dielectric storage material disposed upona portion of the faces of said grooves so that the major portion of theexposed surface of said dielectric storage material lies below saidplane.

References Cited by the Examiner UNITED STATES PATENTS 2,538,836 1/1951Jensen 313-89 2,734,145 2/1956 Reed 313329 X 2,790,228 4/ 1957 Koda eta1 29-25.17 2,859,376 11/1958 Kirkpatrick 313-89 X 2,926,419 3/ 1960Harris 2925.17 2,979,633 4/1961 Harris 313-89 JOHN W. HUCKERT, PrimaryExaminer.

RALPH G. NILSON, DAVID J. GALVIN, Examiners.

1. A STORAGE TARGET COMPRISING A BASE MEMBER HAVING A ROUGHENED SURFACEAND A COATING OF DIELECTRIC STORAGE MATERIAL IN CONTACT WITH SAIDROUGHENED SURFACE, SAID DIELECTRIC MATERIAL BEING DISPOSED IN PORTIONSOF THE ROUGHENED SURFACE WHICH ARE TRANSVERSE TO THE PLANE OF SAID BASEMEMBER AND SO THAT THE EXPOSED SURFACE OF SAID DIELECTRIC MATERIALSUBSTANTIALLY FOLLOWS THE CONTOUR OF SAID ROUGHENED SURFACE.